1. Field of the Invention
This invention relates to an antenna, more particularly, to a composite antenna used in a radio transceiver.
2. Description of the Prior Art
Radio transceivers, such as mobile phones, are quite popular among people for their portability. When using a radio transceiver in a car, car antennas are used for enhancing the efficiency in radio transmission. Most radio transceivers are equipped with an internal antenna switch for selecting its own local antenna or the car antenna. When an antenna connector of a car antenna is connected to the antenna switch of a radio transceiver, the antenna switch will disconnect its local antenna so that radio signals can be transmitted through the car antenna instead of through its local antenna.
Please refer to FIG. 1. FIG. 1 shows a prior art radio transceiver 10 equipped with an antenna switch 14. The radio transceiver 10 comprises a housing 12 and an antenna switch 14 inside the housing 12 for connecting the radio transceiver 10 to a local antenna 16 or a car antenna 18. When the antenna connector 20 of the car antenna 18 is plugged into the antenna switch 14, the signal line 22 in the radio transceiver 10 will be electrically connected to the car antenna 18 so that the radio transceiver 10 can send or receive radio signals through the high efficient car antenna 18. When the antenna connector 20 of the car antenna 18 is disconnected with the antenna switch 14, the signal line 22 will be electrically connected to the local antenna 16. One drawback of the radio transceiver 10 is that it uses the antenna switch 14 to select its local antenna 16 or the car antenna 18. The antenna switch 14 increases the cost and the complexity of the radio transmission circuit of the radio transceiver 10.